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• Sync Audio/Video in MP4 using AutoGen FFmpeg library

  12 juillet 2016, par williamtroup

  I’m currently having problems making my audio and video streams stay synced.

  These are the AVCodecContexts I’m using :

  For Video :

  AVCodec* videoCodec = ffmpeg.avcodec_find_encoder(AVCodecID.AV_CODEC_ID_H264)
  
  AVCodecContext* videoCodecContext = ffmpeg.avcodec_alloc_context3(videoCodec);
  
  videoCodecContext->bit_rate = 400000;
  
  videoCodecContext->width = 1280;
  
  videoCodecContext->height = 720;
  
  videoCodecContext->gop_size = 12;
  
  videoCodecContext->max_b_frames = 1;
  
  videoCodecContext->pix_fmt = videoCodec->pix_fmts[0];
  
  videoCodecContext->codec_id = videoCodec->id;
  
  videoCodecContext->codec_type = videoCodec->type;
  
  videoCodecContext->time_base = new AVRational
  
  {
  
      num = 1,
  
      den = 30
  
  };

  For Audio :

  AVCodec* audioCodec = ffmpeg.avcodec_find_encoder(AVCodecID.AV_CODEC_ID_AAC)
  
  AVCodecContext* audioCodecContext = ffmpeg.avcodec_alloc_context3(audioCodec);
  
  audioCodecContext->bit_rate = 1280000;
  
  audioCodecContext->sample_rate = 48000;
  
  audioCodecContext->channels = 2;
  
  audioCodecContext->channel_layout = ffmpeg.AV_CH_LAYOUT_STEREO;
  
  audioCodecContext->frame_size = 1024;
  
  audioCodecContext->sample_fmt = audioCodec->sample_fmts[0];
  
  audioCodecContext->profile = ffmpeg.FF_PROFILE_AAC_LOW;
  
  audioCodecContext->codec_id = audioCodec->id;
  
  audioCodecContext->codec_type = audioCodec->type;

  When writing the video frames, I setup the PTS position as follows :

  outputFrame->pts = frameIndex;  // The current index of the image frame being written

  I then encode the frame using avcodec_encode_video2(). After this, I call the following to setup the time stamps :

  ffmpeg.av_packet_rescale_ts(&packet, videoCodecContext->time_base, videoStream->time_base);

  This plays perfectly.

  However, when I do the same for audio, the video plays in slow motion, plays the audio first and then carry’s on with the video afterwards with no sound.

  I cannot find an example anywhere of how to set pts/dts positions for video/audio in an MP4 file. Any examples of help would be great !

  Also, I’m writing the video frames first, after which (once they are all written) I write the audio. I’ve updated this question with the adjusted values suggested in the comments.

  I’ve uploaded a test video to show my results here : http://www.filedropper.com/test_124

• C++ h264 ffmpeg/libav encode/decode(lossless) issues

  1er février 2017, par MrSmith

  Insights to encode/decode video with ffmpeg h264 (lossless)

  So I got something working on the encoding part, encode an avi in 264 however VLC wont play it, however Totem will.
  Decoding the same file proves troublesome. (I want the exact same data/frame going in as going out), I get these ;

  saving frame   5
  
  Video decoding
  
  [h264 @ 0x1d19880] decode_slice_header error
  
  frame :6
  
  saving frame   6
  
  Video decoding
  
  [h264 @ 0x1d19880] error while decoding MB 15 7, bytestream -27
  
  [h264 @ 0x1d19880] concealing 194 DC, 194 AC, 194 MV errors in I frame
  
  frame :7
  
  saving frame   7
  
  Video decoding
  
  [h264 @ 0x1d19880] decode_slice_header error

  and ultimatly this

  [H264 Decoder @ 0x7f1320766040] frame :11
  
  Broken frame packetizing
  
  [h264 @ 0x1d19880] SPS changed in the middle of the frame
  
  [h264 @ 0x1d19880] decode_slice_header error
  
  [h264 @ 0x1d19880] no frame!
  
  Error while decoding frame 11

  GAME OVER.

  Now I suspect that I have to go back to 1. the encoding part, there is problary a good reason VLC wont play it !

  I encode like this.

  void encode(char *Y,char *U,char *V){
  
  av_init_packet(&pkt);
  
  pkt.data = NULL;    // packet data will be allocated by the encoder
  
  pkt.size = 0;
  
  fflush(stdout);
  
  
  
  frame->data[0] = (uint8_t*)Y;
  
  frame->data[1] = (uint8_t*)U;
  
  frame->data[2] = (uint8_t*)V;
  
  frame->pts = ++i;
  
  
  
  ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
  
  if (ret < 0) {
  
      fprintf(stderr, "Error encoding frame\n");
  
      exit (EXIT_FAILURE);
  
  }
  
  if (got_output) {
  
      printf("Write frame %3d (size=%5d)\n", i, pkt.size);
  
      fwrite(pkt.data, 1, pkt.size, f);
  
      av_free_packet(&pkt);
  
  }
  
  }

  And the codec is setup like this :

  AVCodecID dasd = AV_CODEC_ID_H264;
  
  codec = avcodec_find_encoder(dasd);
  
  c = avcodec_alloc_context3(codec);
  
  c->bit_rate = 400000;
  
  c->width = 320;
  
  c->height = 240;
  
  c->time_base= (AVRational){1,25};
  
  c->gop_size = 10; 
  
  c->max_b_frames=1;
  
  c->pix_fmt = AV_PIX_FMT_YUV420P;
  
  av_opt_set(c->priv_data, "preset", "slow", 0);
  
  avcodec_open2(c, codec, NULL);

  Since I am going for lossless i am not dealing with delayed frames(is this a correct assumption ?)
  I may not actually be encoding lossless, it seems like I may have to go with something like

  AVDictionary *param;
  
  av_dict_set(&param, "qp", "0", 0);

  And then open...

  So I guess me questions is these :

  • What are the correct codec params for lossless encoding (and advice if h264 is a terrible idea in this regard).
  • Do I need to handle delayed frames when going for lossless ?
  • Why is VLC mad at me ?

  Thanks.

• In using FFmpeg SDK, the mp4 file encoded with HEVC(x265) codec not playing in general player

  26 octobre 2016, par Wiktor Kostus

  Everyone !

  I am going to encode mp4 file (x264 codec) to HEVC(x265) codec using FFmpeg SDK.
  Also, I am going to write the encoded file into .mp4 file container.

  The problem I am facing is that the encoded file is played well in FFplay and VLC player but it isn’t played in general HEVC player.

  I used the general method to encode the codec in FFmpeg SDK. I think I have a mistake to use the avformat_write_header() function. It seems that some parameters to pass AVFormatContext, AVOutputFormat or AVCodecContext for HEVC codec are missing.

  Finally, I would like to know the way to write the HEVC codec into mp4 container. I also would like to know the right parameters related to Context instances for HEVC codec.

  Below is my tiny demo code. (I have skipped the code related to InputStream since I think I have a mistake in OutputStream)

  AVFormatContext* pFormatCtx;
  
  AVOutputFormat* fmt;
  
  AVStream* video_st;
  
  AVCodecContext* pCodecCtx;
  
  
  
  const char* out_file = "output.mp4";
  
  
  
  pFormatCtx = avformat_alloc_context();
  
  fmt = av_guess_format(NULL, out_file, NULL);
  
  pFormatCtx->oformat = fmt;
  
  
  
  if (avio_open(&pFormatCtx->pb, out_file, AVIO_FLAG_READ_WRITE) < 0){
  
      printf("Failed to open output file! \n");
  
      return -1;
  
  }
  
  
  
  video_st = avformat_new_stream(pFormatCtx, 0);
  
  video_st->time_base.num = 1; 
  
  video_st->time_base.den = 25;  
  
  
  
  if (video_st==NULL){
  
      return -1;
  
  }
  
  //Param that must set
  
  pCodecCtx = video_st->codec;
  
  pCodecCtx->codec_id =AV_CODEC_ID_HEVC;
  
  pCodecCtx->codec_id = fmt->video_codec;
  
  pCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;
  
  pCodecCtx->pix_fmt = PIX_FMT_YUV420P;
  
  pCodecCtx->width = in_w;  
  
  pCodecCtx->height = in_h;
  
  pCodecCtx->time_base.num = 1;  
  
  pCodecCtx->time_base.den = 25;  
  
  pCodecCtx->bit_rate = 400000;  
  
  pCodecCtx->gop_size=250;
  
  pCodecCtx->qmin = 10;
  
  pCodecCtx->qmax = 51;
  
  pCodecCtx->max_b_frames = 1;
  
  
  
  // Set Option
  
  AVDictionary *param = 0;
  
  av_dict_set(&param, "preset", "ultrafast", 0);
  
  av_dict_set(&param, "tune", "zero-latency", 0);
  
  av_dict_set(&param, "x265-params", "crf=25", 0);
  
  
  
  pCodec = avcodec_find_encoder(pCodecCtx->codec_id);
  
  if (!pCodec){
  
      printf("Can not find encoder! \n");
  
      return -1;
  
  }
  
  if (avcodec_open2(pCodecCtx, pCodec,&param) < 0){
  
      printf("Failed to open encoder! \n");
  
      return -1;
  
  }
  
  
  
  //Write File Header
  
  avformat_write_header(pFormatCtx, NULL); <------ I think it takes any error in here.

  Help me what I am doing wrong.

  Thank you for your consider.